Process for employing an auxiliary anode made of high purity nickel



Oct. 24, 196? F. x. CARLIN 3,349,016

PROCESS FOR EMPLOYING AN AUXILIARY ANODE MADE OF HIGH PURITY NICKEL Filed Jan. 12, 1965 K4 091545 fzs/sm/wr 050/LLQSC P III,IIIIIIIIIIIIIIIIIIII I N V E N TOR. @4405 M14 CApz/N A ow [y United States Patent 3,349,016 PROCESS FOR EMPLOYING AN AUXILIARY ANODE MADE OF HIGH PURITY NICKEL Francis Xavier Carlin, Pompton Lakes, NJ., assignor to The International Nickel Company, Inc., New York, N.Y., a corporation of Delaware Filed Jan. 12, 1965, Ser. No. 425,012 2 Claims. (Cl. 20449) The present invention is directed to the electrodeposition of nickel wherein an auxiliary anode is employed and is directed, more particularly, to such a process wherein an auxiliary anode of high purity nickel is employed.

In the electrodeposition of nickel for decorative purposes, it is known that difiiculties are encountered in securing adequate deposition of nickel at recessed portions of the work. Thus, the throwing power of nickel plating electrolytes is, in many instances, insufiicient to provide a satisfactory nickel coating upon recessed portions of the work being plated without plating an excessive amount of nickel on the portions of the work which are closer to the anode surface. This problem has long been recognized in the art and many solutions have been proposed therefor. Thus, the use of auxiliary anodes in order to overcome the problem has long been known. In many situations, it is possible to employ insoluble anodes such as chromium plated steel, stainless steel, lead, etc. Insoluble anodes, however, are attended by disadvantages in the common or usual chloridecontaining nickel plating solutions in that chlorine is evolved from the surface of the insoluble anode during plating. Accordingly, it is advantageous in many situations to employ a high purity nickel, e.g., electrolytic nickel, as an auxiliary anode. When a high purity nickel material is employed as the auxiliary anode in usual chloride-containing nickel plating baths, it dissolves therein. However, it is found that the anodic corrosion of high purity nickel material, such as electrolytic nickel containing not more than about 0.001% sulfur, tends to proceed unevenly and is attended by the generation of loose metallic nickel. This loose material becomes detached from the anode as corrosion of the anode proceeds and may be deposited upon the cathode surface being plated with the result that a rough nickel plate is produced. This effect is, of course, highly undesirable. It can further be pointed out in this connection that it is a common practice with auxiliary anodes,

whether the anodes are of the insoluble or soluble type,-

to mount the auxiliary anode in its required position with respect to the work by means of a fixture which also holds the work. When this practice is followed, the auxiliary anode remains in place upon the fixture through all of the cleaning and plating operations. In most commercial decorative nickel plating operations, the final plating step is a chromium plating operation and it is found that a nickel auxiliary anode of high purity may be employed satisfactorily in the chromium plating bath as Well as in the nickel plating bath. The fact that the auxiliary anode is mounted directly in the fixture with the work makes it impossible, as a practical matter, to employ anode bags about the auxiliary anode as is done in the case of anodes which remain fixed in their position in the nickel plating tank itself. Accordingly, a problem has remained in the art as to how high purity nickel auxiliary anodes could be employed in nickel plating operations without encountering the production of a metallic sludge.

I have now discovered a means whereby high purity nickel auxiliary anodes may be employed in nickel plating without formation of a metallic sludge as a result of corrosion of the anode.

It is an object of the present invention to provide a process for electrodepositing nickel using a high purity nickel auxiliary anode wherein no production of a finely divided metal sludge is encountered.

Other objects and advantages of the present invention will become apparent from the following description taken in conjunction with the accompanying drawing which illustrates an embodiment of a plating fixtureand circuitry for employing an auxiliary anode made of high purity nickel.

Generally speaking, the present invention contemplates a process for electrodepositing nickel from a nickel plating bath containing at least about 3 grams per liter (g.p.l.) of chloride ion using an auxiliary anode made of high purity nickel wherein the current applied to the auxiliary anode comprises a direct plating current having an anode current density at the auxiliary anode of about 5 to about 75 amperes per square foot and having superimposed upon said direct current (DC) an alternating current (AC) in a ratio of alternating current to direct current of at least 4:1 and with the frequency of the al ternating current being not greater than 20 cycles per second.

It is found that, when the aforementioned conditions are employed, the surface of the high purity nickel auxiliary anode remains smooth and hard during corrosion thereof and that no metallic residue is produced. It is further found that, when the ratio of alternating current to direct current is less than about 4:1 or when the frequency of the alternating current is greater than about 20 cycles per second, the results in accordance with the invention, as indicated by prevention of loose nickel, or metallic sludge, formation, are not achieved. In general, the ratio of alternating current to direct current may be in a range of about 4 to 1 to about 6 to 1 and the frequency range employed for the alternating current may be about 5 cycles per second to about 20 cycles per sec ond, e.g., 5 cycles per second, 15 cycles per second or 20 cycles per second.

In order to give those skilled in the art a better appreciation of the advantages of the invention, the following specific example is given:

A nickel plating bath of the Watts type containing about 330 g.p.l. of nickel sulfate (NiSO .7H O), about 45 g.p.l. of nickel chloride (NiCl .6H O), and about 38 g.p.l. of boric acid, having a pH of about 4 and a temperature of about F. is established. Electrolytic nickel containing about 99.9% nickel and not more than about 0.001% sulfur is employed as an auxiliary anode in fixed relation to a recessed area in work to be plated. Bagged nicked anodes are also employed in the bath. About 10% of the total plating current is supplied to the auxiliary anode with the remainder being supplied to the bagged nickel anodes. Using only direct current at an anode current density of 20 amperes per square foot, it is found that after about two hours of operation, a sponge-like lacy surface is formed upon the electrolytic nickel auxiliary anode material, which surface breaks away during corrosion to produce a metallic residue. A rough cathode deposit is obtained. Alternating current having a frequency of 20 cycles per second and having a current ratio to the direct current of about 4:1 is superimposed on the direct current supplied to the auxiliary anode without any other changes in conditions. Starting with a new cathode, plating is then continued for about 24 hours and it is found the surface of the electrolytic nickel remains smooth and hard, that no production of metallic residue results, and that the nickel deposit at the cathode is smooth.

The accompanying drawing depicts a schematic arrangement for carrying out the present invention, including an exemplary circuit for supplying AC superimposed on DC and including a schematic depiction of an auxiliary anode. assembly 1 connected to the current source. In the drawing, a workpiece having a recessed area is depicted at 11. This workpiece is mounted upon a rack 12 which also has afilxed thereon an auxiliary anode 13 which is mechanically fastened to, and electrically insulated from, rack 12;. As depicted, the assembly is immersed in a plating tank 14. Additional fixed anodes, not shown in the drawing, may also be employed in the bath. The electrical circuit includes an AC source 15 which may be, for example, .an AC generator and amplifier, a commutator and battery, or any other convenient AC source, and a DC source :16 which may be, for example, a battery or a rectifier, etC., which may have the output thereof controlled by a variable resistance 17. Directcurrent may be measured by a DC ammeter 18 and the alternating current by an oscilloscope 19 which is advantageously connected in parallel with a fixed noninductive resistance 20. By means of the auxiliary anode depicted in the drawing, nickel is plated in controlled amounts at and within recessed :areas, such as that depicted in section in the workpiece 11 at the same time nickel is being applied to other portions of the work by means of deposition from other anodes suspended in the tank 14. Superimposed alternating current need only be applied to the auxiliary anode in carrying out the invention and this procedure is advantageous from the standpoint of current economy. The process is operative when the superimposed alternating current is imposed uponall anodes in the plating bath.

It is to be appreciated that any of the usual aqueous acid" chloride-containing nickel plating solutions employed for producting decorative nickel electrodeposits may be employed in carrying out the invention. Thus, the plating bath may be a chloride-sulfate bath, such as the -Watts bath, an all-chloride bath, a sulfamate bath, etc. Such baths contain at least about 3 g.p.l. of chloride ions and, more advantageously, at least about g.p.l. of chloride ions. Satisfactory nickel plating bath compositions contain up to about 400 g.p.l., e.g., about 25 to about 330 g.p.l., of nickel sulfate (NiSO .7H O), about 3 to about 350 g.p.l., e.g., about 10 to about 300 g.p.l., of nickel chloride (NiCl .6H O), up to about 700 g.p.l. of nickel sulfamate, up to about 300 g.p.l. of nickel fiuoborate, and about 25 to about 40 g.p.l. of boric acid. The nickel ion concentration in these baths is about 50 to about 150 g.p.l.; the baths are operated in the pH range of about 1.5 to about 5, at cathode current densities of upto about 300 or 400 amperes per square foot (a.s.f.), and at temperatures from room temperature up 4. to about F. Any of theusual proprietary chloridecontaining semibright and brightnickel plating baths and any of the usual proprietary chromiumplating baths may be employed.

It is to be understood that when the expression high purity nickel is employed herein, reference is made to a nickel material containing not more than about 0.001% sulfur, not more than about 0.03% carbon, not more than about 0.01% copper, not more than about 0.01% iron, not'more than about 0.1% cobalt, and the balance nickel, with the nickel content being at least about 99.85%.

Although the present invention has been described in conjunction with preferred embodiments, it is to be understood that modifications and variations may be resorted to without departing from the spirit and scope of the invention, as those skilled in the art will readily understand. Such modifications and variations are considered to be Within the purview and scope of the invention and appended claims.

I claim:

1.. In the electrodeposition of nickel from a chloride. containing nickel plating bath wherein an auxiliary anode made of high purity nickel containing not more than about 0.001% of sulfur is employed, the improvement comprising supplying to said auxiliary anode a direct current and a superimposed alternating current having a frequency of about 5 cycles per second to about 20 cycles per second and with a current ratio of alternating current to direct current of at least 4 to 1.

2. The process for electrodepositing nickel which comprises fastening an auxiliary anode made of high purity nickel containing not more than about 0.001% sulfur in fixed relation to a recessed area in .work to be plated, immersing said auxiliary anode and said work in a chloride-containing nickel plating bath, supplying to said auxiliary anode a plating current comprising a direct current and a superimposed ,laternating current having a frequency of about 5 cycles per second to 20 cycles per second and with the current ratio of alternating current to direct current being at least about 4 to 1.

References Cited UNITED STATES PATENTS 2,274,056 2/ 1942 Geiger 204--292 2,470,775 3/1949 Jernstedt 204-49 2,706,170 4/ 1955 Marchese 20449 2,951,978 9/ 1960 Dickson et al. 204-49 JOHN H. MACK, Primary Examiner.

T. TUFARIELLO, Assistant Examiner. 

1. IN THE ELECTRODEPOSITION OF NICKEL FROM A CHLORIDECONTAINING NICKEL PLATING BATH WHEREIN AN AUXILIARY ANODE MADE OF HIGH PURITY NICKEL CONTAINING NOT MORE THAN ABOUT 0.001% OF SULFUR IS EMPLOYED, THE IMPROVEMENT COMPRISING SUPPLYING TO SAID AUXILIARY ANODE A DIRECT CURRENT AND A SUPERIMPOSED ALTERNATING CURRENT HAVING A FREQUENCY OF ABOUT 5 CYCLES PER SECOND TO ABOUT 20 CYCLES PER SECOND AND WITH A CURRENT RATIO OF ALTERNATING CURRENT TO DIRECT CURRENT OF AT LEAST 4 TO
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